During maneuvering, it may be necessary for the wheels on opposite sides of a vehicle to rotate at different rates or even in opposite directions. For example, as a four-wheel vehicle rounds a curve, the outer wheels travel a greater distance and therefore must turn faster than the inner wheels. Maneuvering in tight quarters can cause opposing wheels to turn in opposite directions. This presents no difficulties if the wheels are either driven independently or mounted on a dead axle for independent rotation, however, with a live axle some compensation is necessary to permit the wheels to turn at different speeds.
Differentials or differential gearing have long been utilized for distributing power between the wheels while permitting one wheel to turn faster than the other, as needed on curves. The differentials of the prior art typically include a ring gear driven by a pinion gear mounted on the drive shaft. The ring gear is secured to a differential case or housing which rotates therewith. Each axle includes a coaxial bevel gear which meshes at right angles with pinions mounted on spindles within the differential case. When traveling straight ahead, the differential case simply rotates with the ring gear, and there is no relative motion between the pinion and bevel gears therein. When rounding a curve, however, one wheel must travel relatively faster, and the difference in rotation of the axles is compensated for by the pinion gears which permit opposite relative rotation of the bevel gears as the bevel gears are being driven by the differential case such that faster rotation of one axle and wheel is offset by proportionately slower rotation of the other axle and corresponding wheel.
The major disadvantage of conventional differentials has been that all traction can be applied to one axle to the exclusion of the other. That is, if one wheel is slipping on ice or mud while the other wheel is resting on dry pavement, the differential case and pinion gears therein simply turn around the stationary bevel gear for the axle of the wheel with traction on dry pavement while the bevel gear for the axle secured to the wheel on ice spins. The differential thus completely controls the power distributed to the axles and, under certain conditions, all power can be expended on one axle without driving the vehicle.
Various positive or so-called non-slip differentials have been developed to overcome this problem, however, the positive differentials of the prior art have been unnecessarily complex and thus expensive. One of the most popular non-slip differentials of the prior art operates only in forward gear but not in reverse.
There is thus a need for an improved positive differential whereby traction can be applied, regardless of direction, to the other axle if one axle should slip so that neither axle can be driven alone.